The present invention relates to an electronic sphygmomanometer and, more particularly, to an automatic indirect blood pressure measurement system, which displays systolic and diastolic pressure on a digital display panel.
An automatic indirect blood pressure measurement system has been developed, which utilizes the Korotkoff sounds, or blood vessel sounds derived from a microphone positioned under an arm cuff. In such a system, first a high pressure is applied to the arm cuff through the use of an air pump and, then, the pressure applied to the arm cuff is gradually reduced at a rate, for example, 2 to 4 mmHg/sec. During the reduction procedure of the applied pressure, the Korotkoff sounds appear at the systolic pressure point, and the Korotkoff sounds disappear at the diastolic pressure point.
An automatic measurement of the systolic and diastolic pressure can be conducted by detecting the cuff pressure and the Korotkoff sounds. In the most convenient system, the systolic pressure and the diastolic pressure are displayed on the digital display panel.
To ensure stable operation of the blood pressure measurement system of the above-mentioned type, it is necessary that the cuff pressure is first increased to a level higher than the systolic pressure of a person to be detected. And, the system must correctly detect whether the cuff pressure is increasing for preparation purposes or the cuff pressure is decreasing for measurement purposes.
Accordingly, an object of the present invention is to provide an automatic blood pressure measurement system of stable operation.
Another object of the present invention is to provide an initial condition detection system in an automatic blood pressure measurement system for detecting whether the cuff pressure is first increased to a sufficient level.
Still another object of the present invention is to provide an automatic blood pressure measurement control circuit suited for application of the integrated circuit technique.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, the cuff pressure is detected at a predetermined sampling interval. Current cuff pressure is compared with the last cuff pressure in order to determine whether the cuff pressure is increasing for preparation purposes or whether the cuff pressure is decreasing for measurement purposes. Moreover, the difference between the current cuff pressure and the last cuff pressure is calculated. The thus obtained difference is compared with a prefixed value in order to prevent erroneous operation due to fluctuation of the cuff pressure.
In a preferred form, a standby detection circuit is incorporated in the blood pressure measurement system in order to determine whether the cuff pressure is first increased to a desired level greater than the systolic pressure of a person to be measured. More specifically, a time interval detection means is provided for detecting a time interval from initiation of the measuring operation to a time at which the first Korotkoff sound appears. When the Korotkoff sound appears before a predetermined time interval has passed, the standby detection circuit determines that the cuff pressure has not been increased to the desired level.
In another preferred form, an auto reset circuit is incorporated in the blood pressure measurement system, which functions to automatically reset the system when the cuff pressure is reduced to a predetermined value, for example, 20 mmHg.